Ferrite is a generic term for any compound including an oxide of a divalent cationic metal and trivalent iron, and ferrite magnets have found a wide variety of applications in numerous types of rotating machines, loudspeakers, and so on. Typical materials for a ferrite magnet include Sr ferrites (SrFe12O19) and Ba ferrites (BaFe12O19) having a hexagonal magnetoplumbite structure. Each of these ferrites is made of iron oxide and a carbonate of strontium (Sr), barium (Ba) or any other suitable element, and can be produced at a relatively low cost by a powder metallurgical process.
Recently, it was proposed that the coercivity HcJ and the remanence Br of an Sr ferrite be increased by substituting a rare-earth element such as La for a portion of Sr and by substituting Co for a portion of Fe (see Patent Documents Nos. 1 and 2).
Just like the Sr ferrite, it was also proposed that a rare-earth element such as La be substituted for a portion of Ca in a Ca ferrite and that Co be substituted for a portion of Fe (see Patent Document No. 3).                Patent Document No. 1: Japanese Patent Application Laid-Open Publication No. 10-149910        Patent Document No. 2: Japanese Patent Application Laid-Open Publication No. 11-154604        Patent Document No. 3: Japanese Patent Application Laid-Open Publication No. 2000-223307        